package main

import (
	"context"
	"fmt"
	"time"

	"github.com/spf13/cobra"
	"golang.org/x/sync/errgroup"

	"github.com/restic/restic/internal/backend"
	"github.com/restic/restic/internal/debug"
	"github.com/restic/restic/internal/errors"
	"github.com/restic/restic/internal/repository"
	"github.com/restic/restic/internal/restic"
	"github.com/restic/restic/internal/walker"
)

var cmdRewrite = &cobra.Command{
	Use:   "rewrite [flags] [snapshotID ...]",
	Short: "Rewrite snapshots to exclude unwanted files",
	Long: `
The "rewrite" command excludes files from existing snapshots. It creates new
snapshots containing the same data as the original ones, but without the files
you specify to exclude. All metadata (time, host, tags) will be preserved.

The snapshots to rewrite are specified using the --host, --tag and --path options,
or by providing a list of snapshot IDs. Please note that specifying neither any of
these options nor a snapshot ID will cause the command to rewrite all snapshots.

The special tag 'rewrite' will be added to the new snapshots to distinguish
them from the original ones, unless --forget is used. If the --forget option is
used, the original snapshots will instead be directly removed from the repository.

Please note that the --forget option only removes the snapshots and not the actual
data stored in the repository. In order to delete the no longer referenced data,
use the "prune" command.

EXIT STATUS
===========

Exit status is 0 if the command was successful, and non-zero if there was any error.
`,
	DisableAutoGenTag: true,
	RunE: func(cmd *cobra.Command, args []string) error {
		return runRewrite(cmd.Context(), rewriteOptions, globalOptions, args)
	},
}

type snapshotMetadata struct {
	Hostname string
	Time     *time.Time
}

type snapshotMetadataArgs struct {
	Hostname string
	Time     string
}

func (sma snapshotMetadataArgs) empty() bool {
	return sma.Hostname == "" && sma.Time == ""
}

func (sma snapshotMetadataArgs) convert() (*snapshotMetadata, error) {
	if sma.empty() {
		return nil, nil
	}

	var timeStamp *time.Time
	if sma.Time != "" {
		t, err := time.ParseInLocation(TimeFormat, sma.Time, time.Local)
		if err != nil {
			return nil, errors.Fatalf("error in time option: %v\n", err)
		}
		timeStamp = &t
	}
	return &snapshotMetadata{Hostname: sma.Hostname, Time: timeStamp}, nil
}

// RewriteOptions collects all options for the rewrite command.
type RewriteOptions struct {
	Forget bool
	DryRun bool

	Metadata snapshotMetadataArgs
	restic.SnapshotFilter
	excludePatternOptions
}

var rewriteOptions RewriteOptions

func init() {
	cmdRoot.AddCommand(cmdRewrite)

	f := cmdRewrite.Flags()
	f.BoolVarP(&rewriteOptions.Forget, "forget", "", false, "remove original snapshots after creating new ones")
	f.BoolVarP(&rewriteOptions.DryRun, "dry-run", "n", false, "do not do anything, just print what would be done")
	f.StringVar(&rewriteOptions.Metadata.Hostname, "new-host", "", "replace hostname")
	f.StringVar(&rewriteOptions.Metadata.Time, "new-time", "", "replace time of the backup")

	initMultiSnapshotFilter(f, &rewriteOptions.SnapshotFilter, true)
	initExcludePatternOptions(f, &rewriteOptions.excludePatternOptions)
}

type rewriteFilterFunc func(ctx context.Context, sn *restic.Snapshot) (restic.ID, error)

func rewriteSnapshot(ctx context.Context, repo *repository.Repository, sn *restic.Snapshot, opts RewriteOptions) (bool, error) {
	if sn.Tree == nil {
		return false, errors.Errorf("snapshot %v has nil tree", sn.ID().Str())
	}

	rejectByNameFuncs, err := opts.excludePatternOptions.CollectPatterns()
	if err != nil {
		return false, err
	}

	metadata, err := opts.Metadata.convert()

	if err != nil {
		return false, err
	}

	var filter rewriteFilterFunc

	if len(rejectByNameFuncs) > 0 {
		selectByName := func(nodepath string) bool {
			for _, reject := range rejectByNameFuncs {
				if reject(nodepath) {
					return false
				}
			}
			return true
		}

		rewriter := walker.NewTreeRewriter(walker.RewriteOpts{
			RewriteNode: func(node *restic.Node, path string) *restic.Node {
				if selectByName(path) {
					return node
				}
				Verbosef(fmt.Sprintf("excluding %s\n", path))
				return nil
			},
			DisableNodeCache: true,
		})

		filter = func(ctx context.Context, sn *restic.Snapshot) (restic.ID, error) {
			return rewriter.RewriteTree(ctx, repo, "/", *sn.Tree)
		}
	} else {
		filter = func(_ context.Context, sn *restic.Snapshot) (restic.ID, error) {
			return *sn.Tree, nil
		}
	}

	return filterAndReplaceSnapshot(ctx, repo, sn,
		filter, opts.DryRun, opts.Forget, metadata, "rewrite")
}

func filterAndReplaceSnapshot(ctx context.Context, repo restic.Repository, sn *restic.Snapshot,
	filter rewriteFilterFunc, dryRun bool, forget bool, newMetadata *snapshotMetadata, addTag string) (bool, error) {

	wg, wgCtx := errgroup.WithContext(ctx)
	repo.StartPackUploader(wgCtx, wg)

	var filteredTree restic.ID
	wg.Go(func() error {
		var err error
		filteredTree, err = filter(ctx, sn)
		if err != nil {
			return err
		}

		return repo.Flush(wgCtx)
	})
	err := wg.Wait()
	if err != nil {
		return false, err
	}

	if filteredTree.IsNull() {
		if dryRun {
			Verbosef("would delete empty snapshot\n")
		} else {
			h := backend.Handle{Type: restic.SnapshotFile, Name: sn.ID().String()}
			if err = repo.Backend().Remove(ctx, h); err != nil {
				return false, err
			}
			debug.Log("removed empty snapshot %v", sn.ID())
			Verbosef("removed empty snapshot %v\n", sn.ID().Str())
		}
		return true, nil
	}

	if filteredTree == *sn.Tree && newMetadata == nil {
		debug.Log("Snapshot %v not modified", sn)
		return false, nil
	}

	debug.Log("Snapshot %v modified", sn)
	if dryRun {
		Verbosef("would save new snapshot\n")

		if forget {
			Verbosef("would remove old snapshot\n")
		}

		if newMetadata != nil && newMetadata.Time != nil {
			Verbosef("would set time to %s\n", newMetadata.Time)
		}

		if newMetadata != nil && newMetadata.Hostname != "" {
			Verbosef("would set hostname to %s\n", newMetadata.Hostname)
		}

		return true, nil
	}

	// Always set the original snapshot id as this essentially a new snapshot.
	sn.Original = sn.ID()
	sn.Tree = &filteredTree

	if !forget {
		sn.AddTags([]string{addTag})
	}

	if newMetadata != nil && newMetadata.Time != nil {
		Verbosef("setting time to %s\n", *newMetadata.Time)
		sn.Time = *newMetadata.Time
	}

	if newMetadata != nil && newMetadata.Hostname != "" {
		Verbosef("setting host to %s\n", newMetadata.Hostname)
		sn.Hostname = newMetadata.Hostname
	}

	// Save the new snapshot.
	id, err := restic.SaveSnapshot(ctx, repo, sn)
	if err != nil {
		return false, err
	}
	Verbosef("saved new snapshot %v\n", id.Str())

	if forget {
		h := backend.Handle{Type: restic.SnapshotFile, Name: sn.ID().String()}
		if err = repo.Backend().Remove(ctx, h); err != nil {
			return false, err
		}
		debug.Log("removed old snapshot %v", sn.ID())
		Verbosef("removed old snapshot %v\n", sn.ID().Str())
	}
	return true, nil
}

func runRewrite(ctx context.Context, opts RewriteOptions, gopts GlobalOptions, args []string) error {
	if opts.excludePatternOptions.Empty() && opts.Metadata.empty() {
		return errors.Fatal("Nothing to do: no excludes provided and no new metadata provided")
	}

	var (
		repo   *repository.Repository
		unlock func()
		err    error
	)

	if opts.Forget {
		Verbosef("create exclusive lock for repository\n")
		ctx, repo, unlock, err = openWithExclusiveLock(ctx, gopts, opts.DryRun)
	} else {
		ctx, repo, unlock, err = openWithAppendLock(ctx, gopts, opts.DryRun)
	}
	if err != nil {
		return err
	}
	defer unlock()

	snapshotLister, err := restic.MemorizeList(ctx, repo, restic.SnapshotFile)
	if err != nil {
		return err
	}

	bar := newIndexProgress(gopts.Quiet, gopts.JSON)
	if err = repo.LoadIndex(ctx, bar); err != nil {
		return err
	}

	changedCount := 0
	for sn := range FindFilteredSnapshots(ctx, snapshotLister, repo, &opts.SnapshotFilter, args) {
		Verbosef("\n%v\n", sn)
		changed, err := rewriteSnapshot(ctx, repo, sn, opts)
		if err != nil {
			return errors.Fatalf("unable to rewrite snapshot ID %q: %v", sn.ID().Str(), err)
		}
		if changed {
			changedCount++
		}
	}

	Verbosef("\n")
	if changedCount == 0 {
		if !opts.DryRun {
			Verbosef("no snapshots were modified\n")
		} else {
			Verbosef("no snapshots would be modified\n")
		}
	} else {
		if !opts.DryRun {
			Verbosef("modified %v snapshots\n", changedCount)
		} else {
			Verbosef("would modify %v snapshots\n", changedCount)
		}
	}

	return nil
}
